The present invention relates to a multilayered resin plate of the cured-layer superposition type which has excellent flatness and is suitable for use in, e.g., optical applications such as cell substrates, touch panels, electromagnetic shields, and solar cell covers. The invention further relates to a process for producing the resin plate.
With the trend toward size increase in liquid-crystal displays, cell substrates are required to be thinner and more lightweight. Under these circumstances, there is a desire for a resin substrate usable as a substitute for glass substrates, and thermoset epoxy resin plates excellent in heat resistance and optical properties are expected to be promising. This is because the thermoplastic resin films used as cell substrates in portable telephones and the like are so insufficient in rigidity that it is difficult to maintain a cell gap and to obtain a liquid-crystal cell having a size of 2 inches or larger.
However, the conventional thermoset epoxy resin plates produced through casting or the like not only are unsuitable for mass production but have a problem that the resin plates obtained are apt to have an undulation due to internal strain resulting from, e.g., time differences in thermal curing and hence have poor flatness. Such undulation becomes severer as the thickness of the resin plates increases especially in the range of thicknesses not smaller than 100 xcexcm, which is required of cell substrates and the like, and as the substrate size increases. This undulation has been a serious obstacle to the use of those thermoset epoxy resin plates in applications such as cell substrates.
An object of the invention is to provide a cured resin plate which is reduced in undulation and has excellent flatness even when having a thickness of 100 xcexcm or larger or a size exceeding 2 inches. Another object of the invention is to provide a process for efficiently mass-producing the resin plate.
The invention provides a process for producing a multilayered resin plate which comprises spreading a resinous coating fluid A on a support having a smooth surface to form an unsolidified or solidified coating layer, spreading thereon a resinous coating fluid B which is the same as or different from the coating fluid A to form two or more superposed layers of the coating fluid B, and solidifying the layers separately or simultaneously to thereby form superposed resin layers adhered to each other which comprise two or more adjacent cured resin layers. The invention further provides a multilayered resin plate comprising superposed layers adhered to each other which are composed of a thermoset epoxy resin layer and superposed thereon a thermoset epoxy resin layer having a smaller thickness than that layer.
According to the invention, a multilayered resin plate can be continuously mass-produced highly efficiently by the process in which resinous coating fluids are spread. Since the cured resin plate obtained comprises cured resin layers superposed on each other, it can be reduced in undulation and has excellent flatness even when having a thickness as large as 100 xcexcm or more or having a large area with a size exceeding 2 inches.